The invention relates to a cutter for cutter-bar mowers of harvesting machines and to a process for producing it. Cutters for cutter-bar mowers are used in a wide variety of designs both as an individual cutter and as a multiple cutter. The most common cutters are those produced as drop forgings or as castings. They consist essentially of the stable cutter bottom part screwed at its rear end to the cutter-bar, the cutter tip tapering to a point and directed forwards, and the cutter lip or cutter top part which extends to the rear from the cutter tip and which forms with the cutter bottom part a gap in which the knife blade is moved to and fro. The cutter top part, also called a cutter lip, is connected firmly at one end to the cutter tip or is made in one piece with it. In most cases, the top part is formed when the knife-blade gap is milled out of the cutter forged as a whole.
Other embodiments of cutters for cutter-bar mowers are described in Australian Patent Specification No. 43,403/68 and in German Offenlegungsschrift No. 2,855,234.
They consist of stampings which have been obtained as a result of the stamping out of flat material of suitable thickness. Two or more stampings are connected to one another by means of welding, riveting or screwing to form an individual or multiple cutter (as a rule a double cutter). In such an embodiment, the cutter bottom part and cutter top part are connected in front of the blade gap, where the two parts rest flat on one another. This connecting region at the same time forms the cutter tip, whilst the other ends of the bottom cutter and top cutter are screwed to the cutter bar, that is to say behind the knife-blade gap. As a rule, the knife gap is formed as a result of the bending of either the top cutter or the bottom cutter or, if appropriate, both of these.
Although, in such a known embodiment, the form of the cutter tip tapering in the form of a wedge is of very stable design in a horizontal direction, nevertheless the stability is not very high in a vertical direction, in particular being based only on the material thickness of the cutter top part and cutter bottom part which are connected to one another in this region located in front of the knife gap.
This low stability in a vertical direction has a particularly adverse effect on the cutter tip. When the tip strikes against an obstacle under rough operating conditions in the field, such as, for example, a stone or other foreign bodies, the tip easily breaks off or is warped. Furthermore, as regards cutters to which grain lifters are fastened, the tips of the cutters are broken off very easily when a grain lifter is overloaded and thereby pulled downwards.
These single, double or multiple cutters produced from flat material, in which the cutter top part is extended up to the cutter bar and is fastened there in the same way as the cutter bottom part, have per se an extremely high stability both in a horizontal and in a vertical direction. As mentioned above, only the cutter tip constitutes a weak point.
In the applicant's own older patent application No. P 32 30 882.5, it is proposed, to eliminate this weak point, that the cutter top part and/or the cutter bottom part, which are produced from flat material, be shaped in front of the knife gap and then welded by suitable means. As a result of this shaping, the tip acquires very high stability.
According to a preferred embodiment, the top part of the cutter is straight and the bottom part is twisted. As a result, the bottom part acquires a sharp edge as a bearing point on the top part. This sharp edge is very well suited to be welded to the top part by means the so-called resistant projection welding. The edge represents as it were the projection necessary for welding.
In another embodiment, the top part is twisted and the bottom part is flat. In this case, welding is the same as in the opposite case mentioned above. In further exemplary embodiments, the tip of the cutter top part and/or the tip of the cutter bottom part has a crescent-shaped cross-section, so that there are always two edges available for resistance welding by the projection welding process.
It has now been shown that this welding results in a small joint at the cutter tip, and since this has a very disturbing effect on some types of grain or grass it has to be ground away. A relatively large amount of material has to be ground away in order to give the cutter tip the best possible shape.
A further disadvantage is that, because of the relatively thin components, case-hardening penetrates to a relatively great depth at the tip of the cutter, as a result of which the tip becomes very hard and the danger of breakage therefore increases.
On the other hand, attempts were also made to make the complete connection between the top cutter and bottom cutter by means of arc welding. However, a relatively large amount of welding material, that is to say electrode material, is required for closing the wedge-shaped gap at the tip of the cutter, so that this process is unsuitable for economic reasons.